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Buick LH6 specs: 325 ci (5.3L) 8-cylinder, 3.78 x 3.622 in (96 x 92 mm) bore and stroke, 9.9:1 compression. Rated 300 hp, 2005–2007.
The Buick 325ci (LH6) is close to square: 3.7799" bore against 3.622" stroke, within 4.4%, which splits the difference between a high-revving layout and a torque layout. The 3.622" stroke puts mean piston speed at 4,000 ft/min around 6,650 RPM, which is where a production bottom end is generally considered at its limit. A rod ratio of 1.684 is in the range most production engines fall in. Each of the 8 cylinders displaces 40.6 ci (666 cc).
9.9:1 on aluminum heads is in the range that usually runs on pump premium; aluminum sheds heat faster than iron, which makes the same number a little more forgiving.
It is one of 2 engines in the Buick 325ci family, all of them 325 ci — the differences between them are in compression, heads and rating, not displacement. 3 factory variants share these dimensions, rated at 300 hp across 2005–2007.
| Displacement | 325 ci / 5.3 L |
|---|---|
| Bore | 3.7799" |
| Stroke | 3.622" |
| Cylinders | 8 |
| Configuration | V8 |
| Compression ratio | 9.9:1 |
| Rod length | 6.098" |
| Rod ratio | 1.684 |
| Bore/stroke ratio | 1.044 |
| Block material | aluminum |
|---|---|
| Head material | aluminum |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 300 hp |
| Years | 2005–2007 |
| Year | Version | HP @ rpm | Torque @ rpm | Comp. |
|---|---|---|---|---|
| 2006 | LH6 net | 300 @ 5200 | 330 lb-ft @ 4000 | — |
Factory specification sheet.
| Bore/stroke character | 1.044 — square — bore and stroke are within 5%, a balanced compromise |
|---|---|
| Mean piston speed at 6,000 RPM | 3,622 ft/min — in the range typical of performance street engines |
| Rod ratio | 1.684 — moderate — the range most production V8s fall in |
| Displacement per cylinder | 40.6 ci |
| Static compression | 9.9:1 — in the range that usually runs on pump premium |
Each link opens the calculator with this engine's specs already filled in.
These records share identical bore, stroke, displacement and compression. They differ by model year and factory power rating.
| Year | Advertised HP | Code |
|---|---|---|
| 2005 | 300 hp | LH6 |
| 2006 | 300 hp | LH6 |
| 2007 | 300 hp | LH6 |
5 factory vehicles, 2005–2009. Each year opens that model's engine table.